Allow to use of GIF images in LVGL. Based on https://github.com/lecram/gifdec
When enabled in `lv_conf.h` with `LV_USE_GIF``lv_gif_create(parent)` can be used to create a gif widget.
`lv_gif_set_src(obj, src)` works very similarly to `lv_img_set_src`. As source It also accepts images as variables (`lv_img_dsc_t`) or files.
## Convert GIF files to C array
To convert a GIF file to byte values array use [LVGL's online converter](https://lvgl.io/tools/imageconverter). Select "Raw" color format and "C array" Output format.
Note that, a file system driver needs to be registered to open images from files. Read more about it [here](https://docs.lvgl.io/master/overview/file-system.html) or just enable one in `lv_conf.h` with `LV_USE_FS_...`